Patients with heart disease may have myocardial ischemia or left ventricular dysfunction without symptoms. We studied the exercise responses of 14 asymptomatic patients with significant aortic stenosis with valve gradients ranging from 40 to 144 mmHg, using treadmill testing, thallium-201 scintigraphy, and radionuclide angiography. Compared to age and gender-matched controls, patients with aortic stenosis demonstrated reduced exercise tolerance and maximum oxygen consumption associated with a lower peak systolic blood pressure response to exercise. Ten of 14 patients demonstrated ischemic-appearing ECG responses to exercise, of whom only 3 had reversible thallium defects. Radionuclide angiographic studies showed that aortic stenosis patients tended to have higher left ventricular ejection fractions at rest and significantly lower early peak filling rates suggesting abnormal diastolic function at rest, compared to controls. During maximum supine exercise, aortic stenosis patients had less of an increase in left ventricular ejection fraction associated with a decrease in end-diastolic volume and stroke volume from baseline measurements compared to controls who increased end-diastolic volume and stroke volume during exercise. The abnormal volume changes during exercise correlated directly with effort limitation in these patients. Thus, despite the absence of symptoms, patients with aortic stenosis demonstrated limited effort tolerance with abnormal systemic and left ventricular hemodynamics, which is most likely a consequence of inability to augment end-diastolic volume during exercise.